The prognostic role of soluble transforming growth factor-β (sTGFb) and soluble programmed death-ligand 1 (sPDL1) in biliary tract cancer patients treated with binimetinib and capecitabine.

257 Background: Transforming growth factor (TGF) -β signaling is important for tumor growth and metastasis in biliary tract cancer (BTC). TGF-β attenuates tumor response to programmed death-ligand 1 (PD-L1) blockade. This study aimed to evaluate a correlation between soluble TGF-β (s TGF-β) and soluble PD-L1 (sPD-L1) and its prognostic role in BTC. Methods: Study population consisted of 34 patients enrolled in phase Ib clinical trial of binimetinib (MEK inhibitor) with capecitabine in gemcitabine-pretreated BTC (ClinicalTrials.gov: NCT02773459). Blood samples at screening, after first cycle, after second cycle, and at disease progression were prospectively collected. Plasma sTGF-β and sPD-L1 values were measured by using an enzyme-linked immunosorbent assay. Results: In total 34 patients, 25 (73.5%) and 9 patients (26.5%) were second-line and third-line setting, respectively. Median progression-free survival (PFS) and overall survival (OS) were 4.1 and 7.8 months. The mean baseline sTGF-β and sPD-L1 were 18.7 ng/ml and 3.1 ng/ml. There was a positive correlation between sTGF-β and sPD-L1 value (pearson correlation = 0.596, p < 0.001). Mean baseline value was likely to be higher in best response of progressive disease, followed by stable disease and partial response. Similarly, higher baseline sTGF-β showed significantly shorter PFS (3.4 vs 5.1 months (m), p = 0.047) and OS (5.4 vs 9.7 m, p = 0.042). Higher baseline sPD-L1 also had a trend for poor PFS and OS (PFS: 3.0 vs 4.3 m, p = 0.220; OS: 6.4 vs 9.7 m, p = 0.140). Regarding changes from baseline to after first cycle, sTGF-β change of > 3.6 ng/ml demonstrated significantly shorter OS (5.9 vs 10.8 m, p = 0.020), although PFS did not differ according to sTGF-β change (p = 0.210). In contrast, OS did not differ according to sPD-L1 change (p = 0.190). sPD-L1 change > -1.7 ng/ml even had longer PFS (5.1 vs 2.2 m, p = 0.005). Conclusions: In BTC patients with binimetinib and capecitabine, there is a positive correlation between sTGF-β and sPD-L1 value and higher baseline sTGF-β and sPD-L1 indicate a worse prognosis. The early change of sTGF-β and sPD-L1 during treatment could predict the survival.